Removal of arteriovenous malformation

Arteriovenous malformation or AVM is abnormal blood vessels that consist of a blood vessel "nidus" (nest) through which arteries connect directly to veins, instead of through capillaries. Some people are born with the nidus, but as the years go by, it tends to expand, as the veins that drain the area cannot handle the pressure of the arterial vessels. This causes large worm-like vessels to develop (malform) that can cause a bleeding at some future time. These lesions are surrounded by a very discrete layer of abnormal, nonfunctioning brain tissue, thus allowing their removal with relative safety to the surrounding brain.

More information about arteriovenous malformation can be found here